Present day image reproduction systems, such as those employed in the entertainment industry, where large multicolor images may be recreated on a variety of image reproduction media, commonly employ one or more laser scanning devices to scan a modulated laser beam across an image projection surface. For optimal control of image reproduction, it is desirable to change the spot size (beam width) of the imaging laser beam and thereby the thickness of a line being imaged onto the reproduction surface. In the past, in order to vary line thickness, it was customary practice to rescan the beam across the imaging medium, with each subsequent scan being slightly offset from a previous scan, thereby widening or thickening the imaged line. Unfortunately, such a technique is extremely slow and detracts from the objective of rapidly displaying an image to a viewing audience.
One proposal to solve this problem, described in the U.S. patent to M. Razzaghi, No. 5,274,492, entitled: "Light Spot Size and Shape Control for Laser Projector," involves the use of a flexible or deformable mirror to change the focus or spread of the scanning beam. Unfortunately, because the principal component employed in this system, the mirror element, is subjected to repetitious physical flexing and heating by the incident beam, it soon develops internal stresses, which not only modify the intended shape of the mirror, but limit its useful life. In addition, because of the heat-induced stress problem, such a scheme is limited to use with only relatively low energy lasers.